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PubMed1999

High-frequency jet ventilation using a helium-oxygen mixture.

The physiological basis for the use of helium relates to the relationship described by Poiseuille. During turbulent gas flow, the factors determining the resistance to flow include the density of gas as well as the length and the radius of a tube. While it may not be possible to readily change the latter two, altering the density of the gas is possible by using helium instead of nitrogen. A helium-oxygen combination has been used most commonly to improve air exchange in patients with upper airway obstruction. Anecdotal reports also suggest the beneficial effects of helium during mechanical ventilation in patients with status asthmaticus, hyaline membrane disease, and other pulmonary parenchymal disorders. To date, the clinical reports have utilized helium only with conventional mechanical ventilation. We present a child whose progressive respiratory failure was treated by using high-frequency jet ventilation with a combination of helium and oxygen. The techniques for the delivery of helium and oxygen through the jet ventilator are discussed.

Helium↗
PubMed1998

Helium gas microbubbles. Experimental study on a new ultrasound contrast material.

PURPOSE: To evaluate histological changes and duration of enhancement after the intra-arterial injection of helium gas microbubbles in comparison with conventionally used carbon dioxide (CO2) microbubbles at US. MATERIAL AND METHODS: Four different doses of helium gas microbubbles (0, 0.1, 0.2 and 0.5 ml/kg) mixed with normal saline and own blood were injected into the celiac artery of 8 rabbits. After one week, autopsies were performed on all animals and histological changes in the liver, stomach and spleen were studied on hematoxylin-eosin stains. In addition, VX-2 tumor strains were transplanted into the femoral muscle in 5 other rabbits. Four weeks after transplantation, we catheterized the femoral artery and either CO2 or helium gas microbubbles were injected under US observation. We evaluated the duration of enhancement in the tumors with the two types of microbubbles. RESULTS: On histological evaluation, damage in hepatic cells as well as multiple areas of gastritis in the stomach were seen when a dose of 0.5 ml/kg of helium gas was used. Damage in the liver and stomach was slight at a dose of 0.2 ml/kg. The spleen was not damaged at doses of under 0.5 ml/kg. In the evaluation of tumor enhancement, the duration of enhancement with helium gas microbubbles ranged from 28 to 45 min (average 36 min) while that with CO2 ranged from 4 to 12 min (average 9 min) (p<0.01 at paired t-test). CONCLUSION: Intra-arterial injection of helium gas should not exceed 0.2 ml/kg: a dose of 0.5 ml/kg may cause damage to the liver and stomach. The duration of enhancement with helium gas microbubbles is significantly longer than that with CO2 microbubbles.

Animals↗
PubMed1953

Effect of helium on the respiration and glycolysis of mouse liver slices.

It has been shown that helium has the ability to affect variously the rates of certain metabolic reactions in vitro as compared to nitrogen. An attempt has been made to approximate the sites of action in mouse liver preparations. The following results have been obtained by the substitution of a mixture of 80 per cent helium and 20 per cent oxygen for air: (a) An increase in the rate of oxygen consumption and carbon dioxide production to the same degree, the respiratory quotient remaining unchanged. (b) A decrease in the magnitude of cyanide inhibition. The effectiveness of helium increases with the degree of the cyanide inhibition. (c) No effect on the activity of slices which have been poisoned with fluoride when either lactate or pyruvate has been added as a substrate. (d) A change in the rate, and the slope of the curve of oxygen consumption in liver homogenates which are utilizing pyruvate as a substrate. The use of helium relative to nitrogen under anaerobic conditions causes: (a) A depression of the glycolytic rates in both mouse liver slices and diaphragm. (b) An increase in the carbon dioxide evolution and lactic acid production of mouse liver homogenates oxidizing either glucose and hexose diphosphate, or hexose diphosphate alone. In neither slices nor homogenates does the addition of fluoride and the use of pyruvate as the hydrogen acceptor alter the fundamental response of the preparations. The following hypotheses have been advanced and discussed in order to explain the observed phenomena: 1. Helium does not alter the substrate utilized by the tissue. 2. The gas interferes in some way with the cyanide-cytochrome oxidase bond, but may not affect cytochrome oxidase in the absence of cyanide. 3. The citric acid cycle is not subject to the influence of helium in tissue slices, but is altered in an unexplained fashion in homogenates. It is postulated that a rearrangement of particulate surfaces may be the significant factor here. 4. The glycolytic cycle is the site of both an inhibitory and an acceleratory effect of helium. The locus of the inhibition lies above the aldolase reaction and that of the acceleration between the aldolase and enolase reactions.

Animals↗
PubMed2001

Is helium insufflation superior to carbon dioxide insufflation in bacteremia and bacterial translocation with peritonitis?

PURPOSE: To evaluate the effects of CO2 or helium insufflation on bacteremia and bacterial translocation in rats with peritonitis. MATERIALS AND METHODS: Forty male Wistar-Albino rats were divided into four groups, each containing 10 rats. The rats in the first group were injected only with E. coli into their peritoneal cavities with no further manipulation. The second group, following E. coli injection, underwent midline laparotomy without manipulation of the viscera for 1 hour. After the injection of E. coli in the third and fourth groups, CO2 and helium pneumoperitoneum, respectively, were maintained for 1 hour under 14 mm Hg pressure. At the end of the sixth hour, tissue samples were taken from the liver, spleen, lung, and mesenteric lymph nodes in order to evaluate bacterial translocation. During the study, blood samples were taken from each rat at 0, 1, 2, 4, and 6 hours to demonstrate bacteremia. RESULTS: There was a significant increase in bacteremia in the CO2 pneumoperitoneum group compared with the laparotomy-only and helium groups at 1 and 2 hours. Although all the blood samples at the fourth hour were positive for E. coli in every rat of all groups, helium was associated with a lower incidence of bacteremia at the sixth hour compared with other groups (P < 0.05). The CO2 pneumoperitoneum caused bacterial translocation to all organs from which tissue samples were taken. Although there was an insignificant decrease in translocation to the liver, spleen, and lung with helium compared with CO2 insufflation, helium did not increase bacterial translocation to the spleen compared with laparotomy alone, as did CO2 (P < 0.05). CONCLUSION: Helium might be an alternative to CO2 insufflation in patients with peritonitis if these results are confirmed by further experimental and clinical trials.

Analysis of Variance↗
PubMed1996

Comparative stress hormone changes during helium versus carbon dioxide laparoscopic cholecystectomy.

Laparoscopic surgery has been termed minimally invasive surgery by advocates of this technology. It has been demonstrated previously that using carbon dioxide for insufflation produces a respiratory acidosis due to transperitoneal absorption of gas. Insufflation with helium does not create this acidosis. We questioned whether laparoscopic surgery would elicit a stress response and whether the absence of acidosis with helium might prevent or reduce the levels of stress hormones. Sixteen female patients undergoing laparoscopic cholecystectomy were randomly assigned to helium (n = 8) or CO2 (n = 8) insufflation. Serum cortisol, epinephrine, and norepinephrine were measured preoperatively, after induction of anesthesia but before insufflation, at 45 min of surgery, and after desufflation. There were increases in epinephrine, norepinephrine, plasma cortisol, and urine cortisol at 45 min and at the conclusion of the procedure over the preoperative value. With ANOVA, each variable showed significant increases from preoperative values, at 45 min, and at the end of the case. Except for the increased epinephrine when helium was used, there were no significant differences in the other variables between helium and CO2. Laparoscopic cholecystectomy produces significant increases in stress hormone levels. Prevention of acidosis with helium insufflation does not appear to protect against increases in stress hormones. Epinephrine levels with helium insufflation are higher than with CO2, and elevations in stress hormones suggest that laparoscopic cholecystectomy is not physiologically minimally invasive.

Acidosis, Respiratory↗
PubMed1994

Helium and lower oxygen concentration do not prolong tracheal tube ignition time during potassium titanyl phosphate laser use.

BACKGROUND: Tracheal tube fire is a well recognized complication of airway laser procedures. The use of helium in the anesthetic gas mixture delays the ignition time of polyvinyl chloride tracheal tubes when a carbon dioxide laser is used. The effects of helium gas mixtures on potassium titanyl phosphate (KTP) laser-induced tracheal tube ignition have not been studied. METHODS: One hundred forty unmarked polyvinyl chloride tracheal tube segments were exposed to KTP or carbon dioxide laser beams. Each tube segment was suspended in a burn chamber with varying mixtures of oxygen in either nitrogen or helium. The gas mixtures were 21%, 30%, and 40% O2 in N2 or 30% and 40% O2 in helium. Fourteen tube segments were tested for each gas mixture. The ignition time was recorded for each segment. The laser beam was turned off at 60 s if ignition did not occur. RESULTS: At 30% O2/N2, mean ignition time with the carbon dioxide laser was 41.3 +/- 10.8 s (mean +/- standard deviation), whereas at 30% O2/He, the mean ignition time was 60 +/- 0 s. Increasing the oxygen concentration to 40% significantly shortened the ignition time with both helium and nitrogen for the carbon dioxide laser. With the KTP laser, ignition time varied greatly at any oxygen concentration. At 30% O2/N2, median ignition time with the KTP laser was 6.9 s (mean time 15.6 +/- 19.5 s), whereas at 30% O2/He, median time was 8.6 s, (mean time 9.9 +/- 5.33 s). No statistically significant differences were found for the ignition times in the KTP laser groups. CONCLUSIONS: Using helium instead of nitrogen with oxygen delays unmarked polyvinyl chloride tracheal tube ignition time when the tube segments are exposed to a carbon dioxide laser beam as compared to a KTP laser. The different laser wavelengths and penetration properties may produce this difference. The helium protocol previously described has been proven safe only with the carbon dioxide laser and should be tested with other laser types before being used clinically with these lasers.

Anesthesia↗
PubMed1990

Effect of helium concentration on experimental upper airway obstruction.

This study investigates the effect of helium concentration in inspired gas on resistance to breathing during experimental upper airway obstruction. Obstruction was modeled by use of a series of four polyvinyl endotracheal tubes narrowed progressively in their midportions with C clamps. Percentage ratios of helium-oxygen gas mixtures were 0:100, 40:60, 60:40, and 80:20. Gas flow was provided by two methods: 1) nontidal flow from compressed gas tanks from which resistance was calculated from pressure and flow measurements, and 2) tidal respiratory flow from human volunteers from whom respiratory effort was evaluated by using airway pressure measurements integrated over 90-second trial periods. The results derived from both methods demonstrated that the effect of helium in reducing resistance and pressure in an obstructed airway is linear (p less than .016) and inversely proportional to helium concentration. Reductions in resistance and pressure were larger for the tighter obstructions (p less than .007). As helium was added to the gas mixture (from 0% to 80%), resistance and airway pressure measurements dropped 42% and 58%, respectively. The major conclusions are that 1) even low concentrations of helium may have therapeutic value and 2) helium is effective only for more severe obstructions.

Adult↗
PubMed2003

Helium pneumoperitoneum ameliorates hypercarbia and acidosis associated with carbon dioxide insufflation during laparoscopic gastric bypass in pigs.

BACKGROUND: In the morbidly obese patient undergoing laparoscopic gastric bypass (LGBP), insufflation with carbon dioxide to 20 mmHg for prolonged periods may induce significant hypercarbia and acidosis with attendant sequelae. We hypothesize that the use of helium as an insufflating agent results in less hypercarbia and acidosis. METHODS: The study was performed between May and November 2002. A Paratrend 7 fiberoptic probe was placed via a carotid artery catheter in 5 adult Yorkshire swine as continuous pH and pCO2 levels were measured. Animals were ventilated to a constant pCO2, after which LGBP was performed. Blood gas values were measured during the procedure and for 1 hour after release of pneumoperitoneum. Helium was used for insufflation in 3 of the pigs and CO2 in 2. Comparison of arterial pH and pCO2 were made between groups. RESULTS: Mean maximum pCO2 for the control group (CO2 insufflation) was 99.75 +/- 22.98 mmHg, while for the experimental group (helium insufflation) was 52.86 +/- 6.27 mmHg (P=.036). Mean low pH for the groups were 7.10 +/-.056 and 7.36 +/-.015 (P =.004) respectively. Normalization of pCO2 in the helium group occurred at a mean of 14.58 min (SD 13.3 min) after release of pneumoperitoneum, while in the control group levels did not normalize (mean final pCO2= 71.5 mmHg). CONCLUSIONS: Helium pneumoperitoneum in LGBP is associated with less intraoperative hypercarbia and acidosis than is the use of CO2. In addition, pCO2 returns to normal more rapidly postoperatively with the use of helium insufflation. Study of helium insufflation in humans undergoing LGBP is needed to prove its benefits in the clinical setting.

Acidosis↗
PubMed1997

[Use of helium-oxygen gas mixtures in acute obstructive respiratory insufficiencies].

Therapeutic use of helium has been described since 1930. Its main action is to reduce bronchial resistances and consequently overall respiratory work. Helium is substituted for nitrogen. The effects of inhaling a helium-oxygen mixture result exclusively from the physicochemical properties of helium: very low density, high kinetic viscosity. With the advent of selective bronchodilators, use of helium was rapidly abandoned until recently with new interest for the treatment of severe acute asthma. We review the literature on the physical properties of helium-oxygen mixtures and propose an analysis of their therapeutic use in severe acute asthma as well as other indications such as acute episodes of obstructive bronchopneumonia and obstruction of the upper airways. Due to the non-invasive nature of this technique, its easy use with spontaneous ventilation and the large body of theoretical data emphasizing its adaptation for therapeutic use, helium-oxygen gas mixtures offer an important therapeutic option for treating severe diseases with poor prognosis. A multicentric national study is under way to validate its use early by emergency ambulatory units for the treatment of severe acute asthma.

Acute Disease↗
PubMed2006

Neutral helium compounds: theoretical evidence for a large class of polynuclear complexes.

Ab initio calculations at the MP2 and CCSD(T) levels of theory disclose the conceivable existence of neutral complexes containing up to four helium atoms. These species are formally obtained by replacing the hydrogen atoms of parent molecules such as CH(4), SiH(4), NH(3), PH(3), H(2)O, H(2)S, C(2)H(2), C(2)H(4), and C(6)H(6) with -NBeHe moieties, which behave as monovalent functional groups containing helium. The geometries and vibrational frequencies of these M(NBeHe)(n) (n>1; M=central moiety) polyhelium complexes have been investigated at the MP2(full)/6-31G(d) level of theory, and their stability with respect to the loss of helium atom(s) has been evaluated by means of single-point calculations at the CCSD(T)/6-311G(d,p) level of theory. Molecules such as H(n)C(NBeHe)(4-n) and H(n)Si(NBeHe)(4-n) (n=0-3), C(2)(NBeHe)(2), and ortho-, meta-, and para-C(6)H(4)(NBeHe)(2) were invariably characterized as energy minima, and were found to be stable with respect to the loss of helium atom(s) by approximately 4-5 kcal mol(-1). On the other hand, species such as C(2)(NBeHe)(4) and C(6)(NBeHe)(6) were characterized as high-order saddle points on the potential-energy surface, and were unstable with respect to helium atom(s) loss owing to the bending motion of the -NBeHe groups. The molecules containing N, P, O, or S as the central atom also showed a variable topology and include second-order saddle points such as S(NBeHe)(2), third-order saddle points such as HN(NBeHe)(2), but also minimum-energy structures such as O(NBeHe)(2) and HP(NBeHe)(2), which are also stable by approximately 5 kcal mol(-1) with respect to the helium atom(s) loss. These results suggest the conceivable existence of an, in principle, very large class of M(NBeHe)(n) (n>1) polyhelium complexes, whose stability may be substantially affected by the nature and the size of the central moiety M. Atoms-in-Molecules (AIM) calculations on selected species invariably suggest that, in our investigated M(NBeHe)(n) (n>1) compounds, the beryllium-helium interaction is essentially electrostatic.

Journal Article↗
PubMed2004

Electron impact ionization in helium nanodroplets: controlling fragmentation by active cooling of molecular ions.

Reported here is a study of the effects of liquid helium cooling on the fragmentation of ions formed by electron impact mass ionization. The molecules of interest are picked up by the helium nanodroplets as they pass through a low pressure oven. Electron impact ionization of a helium atom in the droplet is followed by resonant charge transfer to neighboring helium atoms. When the charge is transferred to the target molecule, the difference in the ionization potentials between helium and the molecule results in the formation of a vibrationally hot ion. In isolation, the hot parent ion would undergo subsequent fragmentation. On the other hand, if the cooling due to the helium is fast enough, the parent ion will be actively cooled before fragmentation occurs. The target molecule used in the present study is triphenylmethanol (TPM), an important species in synthetic chemistry, used to sterically protect hydroxyl groups. Threshold PhotoElectron PhotoIon COincidence (TPEPICO) experiments are also reported for gas-phase TPM to help quantify the ion energetics resulting from the cooling effects of the helium droplets.

Journal Article↗
PubMed2005

Free-energy model for fluid helium at high density.

We present a semianalytical free-energy model aimed at characterizing the thermodynamic properties of dense fluid helium, from the low-density atomic phase to the high-density fully ionized regime. The model is based on a free-energy minimization method and includes various different contributions representative of the correlations between atomic and ionic species and electrons. This model allows the computation of the thermodynamic properties of dense helium over an extended range of density and temperature and leads to the computation of the phase diagram of dense fluid helium, with its various temperature and pressure ionization contours. One of the predictions of the model is that pressure ionization occurs abruptly at rho greater, > or = 10 g cm(-3) , i.e., P greater, > or = 20 Mbar , from atomic helium He to fully ionized helium He2+ , or at least to a strongly ionized state, without a He+ stage, except at high enough temperature for temperature ionization to become dominant. These predictions and this phase diagram provide a guide for future dynamical experiments or numerical first-principle calculations aimed at studying the properties of helium at very high density, in particular its metallization. Indeed, the characterization of the helium phase diagram bears important consequences for the thermodynamic, magnetic, and transport properties of cool and dense astrophysical objects, among which are the solar and the numerous recently discovered extrasolar giant planets.

Journal Article↗
PubMedDate not supplied

Helium leak test for sterility assurance of a sealed bag. II: Establishing a test method for the manufacturing process.

To establish a simpler and more reliable method for retaining the aseptic condition of freeze-dried bulk product of a drug substance, a helium leak test method was developed. The bulk product is for the new kit system for infusion of our antibiotic product. In manufacturing the kit system, the bulk product needs to be transported outside of the aseptic area. We had to use a proper container to enclose the bulk product under aseptic conditions and establish an appropriate method for sterility assurance of the container. We decided to use a flexible aluminum laminate bag as a container and to seal it in a polyethylene bag. To detect tears or pinholes in the bag, a helium leak test was considered. As a tear model, a pinhole of known diameter was made in the aluminum laminate bag which was then filled with helium and sealed in a polyethylene bag. Helium leaking from the pinholes was measured with a helium leak detector, and leakage from a pinhole of more than 50 microm in the aluminum laminate bag could be detected. The amount of leakage was strongly affected by the pinhole diameter, and we developed a scientific approach for measuring leakage using the Poiseiulle Equation. The detection sensitivity of our method was enough to retain an aseptic condition inside the aluminum laminate bag, confirmed by the results of the process simulation test using our helium leak test. We concluded that our helium leak test was useful for sterility assurance of the bulk product sealed in the aluminum laminate bag in the manufacturing process of our kit system for infusion of our antibiotic product.

Quality Control↗
PubMed2001

Helium-oxygen mixture for nonintubated acute asthma patients.

BACKGROUND: Helium and oxygen mixtures (heliox), have been used sporadically in respiratory medicine for decades. Their use in acute respiratory emergencies such as asthma has been the subject of considerable debate. Despite the lapse of more than 60 years since it was first proposed, the role of heliox in treating patients with acute severe asthma is unclear. OBJECTIVES: To determine the effect of the addition of heliox to standard medical care on the course of acute asthma, as measured by pulmonary function testing and clinical endpoints. SEARCH STRATEGY: Randomized controlled trials were identified from the Cochrane Airways Group Asthma Register which is a compilation of systematic searches of CINAHL, EMBASE, MEDLINE, and CENTRAL and hand searching of the 20 most productive respiratory care journals. In addition, primary authors and experts were contacted to identify eligible studies. References from included studies, known reviews and texts were also searched. SELECTION CRITERIA: Inclusion criteria were: 1) randomized, single or double blind, controlled trials; 2) children or adults with a clinical diagnosis of acute asthma seen in emergency departments or equivalent acute care settings; 3) compared treatment with inhaled heliox compared with a control (oxygen or air). Two reviewers independently assessed the studies for inclusion and quality assessment; disagreement was resolved by a third reviewer and consensus. DATA COLLECTION AND ANALYSIS: Data from all included trials were combined using weighted mean differences (WMD), with 95% confidence intervals (95% CI) in a random effects model. Homogeneity of effect sizes were tested with the Dersimonian and Laird method with p<0.1 as the cut point for significance. Sensitivity analyses were performed on age (adults vs. children), different helium-oxygen mixtures and methodological quality. MAIN RESULTS: A total of 4 randomized controlled trials were selected for inclusion with a total of 288 acute asthma patients. Three studies involved adults and one study dealt solely with children. Two were of low quality. The main outcome variable was spirometric measurements (PFT % predicted) in all trials. Pooling the four trials showed no significant differences (WMD = -1.61; 95% CI: -6.64 to 3.41). All pulmonary function tests were recorded during heliox administration (15 to 60 min). There was no evidence of heterogeneity between studies. There were no significant differences between groups when adults vs. children, high vs. low quality, and high vs. low heliox dose studies were compared. The findings were the with a fixed effects model. REVIEWER'S CONCLUSIONS: The existing evidence does not provide support for the administration of helium-oxygen mixtures to patients presenting to the emergency department with moderate to severe acute asthma. Heliox treatment does not have a role in the initial treatment of patients with acute asthma. These conclusions are based upon between-group comparisons and small studies. Additional research in this setting may be warranted.

Acute Disease↗
PubMed2000

Physiological response of rats to delivery of helium and xenon: implications for hyperpolarized noble gas imaging.

The physiological effects of various hyperpolarized helium and xenon MRI-compatible breathing protocols were investigated in 17 Sprague-Dawley rats, by continuous monitoring of blood oxygen saturation, heart rate, EKG, temperature and endotracheal pressure. The protocols included alternating breaths of pure noble gas and oxygen, continuous breaths of pure noble gas, breath-holds of pure noble gas for varying durations, and helium breath-holds preceded by two helium rinses. Alternate-breath protocols up to 128 breaths caused a decrease in oxygen saturation level of less than 5% for either helium or xenon, whereas 16 continuous-breaths caused a 31.5% +/- 2.3% decrease in oxygen saturation for helium and a 30.7% +/- 1. 3% decrease for xenon. Breath-hold protocols up to 25 s did not cause the oxygen saturation to fall below 90% for either of the noble gases. Oxygen saturation values below 90% are considered pathological. At 30 s of breath-hold, the blood oxygen saturation dropped precipitously to 82% +/- 0.6% for helium, and to 76.5% +/- 7. 4% for xenon. Breath-holds longer than 10 s preceded by pre-rinses caused oxygen saturation to drop below 90%. These findings demonstrate the need for standardized noble gas inhalation procedures that have been carefully tested, and for continuous physiological monitoring to ensure the safety of the subject. We find short breath-hold and alternate-breath protocols to be safe procedures for use in hyperpolarized noble gas MRI experiments.

Animals↗
PubMed1992

The output of four modern vaporizers in the presence of helium.

It has been previously demonstrated that the output of calibrated vaporizers is influenced by the concentration of nitrous oxide in the carrier gas. This study was performed to determine whether helium in the carrier gas affects the output of modern calibrated vaporizers. A factorial design was used to determine the influence of carrier-gas helium concentration, carrier-gas flow rate and vaporizer dial setting on the output of four vaporizers: Ohio Calibrated Enflurane, Ohio Calibrated Isoflurane, Ohmeda Isotec 4, and Dräger Vapor 19.1 Isoflurane. Three vaporizers of each model were tested. Output was converted to % of baseline so that different dial settings could be compared. For a given dial setting, baseline was defined as the output at a carrier-gas flow rate of 3 L.min-1 and helium concentration of zero. The data were analyzed using multiple linear regression. There was an effect of helium concentration on vaporizer output in all models. None of these changes was clinically important, since vaporizer output did not vary by more than +/- 10%, except at high flows and at high helium concentrations with the Ohmeda Isotec 4. It is concluded that these vaporizers can be used safely with helium.

Anesthesia, Inhalation↗
PubMed2003

Helium pneumoperitoneum reduces tumor recurrence after curative laparoscopic liver resection in rats in a tumor-bearing small animal model.

BACKGROUND: After exposure of neoplastic tissue to helium, a significant reduction of tumor growth has been detected in experimental studies, both in vitro and in vivo. This tumor-suppressive effect of helium is controversly discussed in the literature. It was therefore the aim of this study to investigate the influence of pneumoperitoneum with CO2, room air, or helium in a tumor-bearing small animal model comparing laparoscopic partial hepatic resection for hepatocellular carcinoma with conventional open partial hepatectomy. METHODS: One-hundred forty-eight male American Cancer Institute rats underwent partial hepatectomy for curative resection of previously induced hepatocellular carcinoma (Morris hepatoma 3924A). Resection was performed either in open laparotomy (n = 30) or laparoscopically under the employment of CO2 (n = 30), room air (n = 30), or helium (n = 30) for the pneumoperitoneum. Twenty-eight animals served as controls receiving anesthesia but no tumor resection. All animals were sacrificed on postoperative days 21, 35, or 56 for autopsy and evaluation of possible tumor recurrence and metastasis. RESULTS: Significant reduction of postoperative tumor recurrence and metastasis was observed in the group of animals receiving laparoscopic tumor resection under helium insufflation compared to open surgery or laparoscopic resection with air pneumoperitoneum. CONCLUSIONS: The results of this study suggest a suppressive effect of helium pneumoperitoneum on postoperative tumor growth and metastatic spread. Furthermore, tumor exposure to room air appears to have a stimulative influence on tumor recurrence and metastasis compared to a pneumoperitoneum established with CO2.

Animals↗
PubMed2005

Noninvasive therapy with helium-oxygen for severe bronchiolitis.

OBJECTIVE: To determine whether noninvasive therapy using a helium-oxygen mixture reduces the use of positive-pressure ventilation in the treatment of respiratory failure caused by severe bronchiolitis. STUDY DESIGN: This was a multicenter, randomized, double-blind, placebo-controlled trial that recruited infants in 4 pediatric intensive care units (PICUs). A total of 39 nonintubated infants with severe bronchiolitis caused by respiratory syncytial virus (RSV) were randomly assigned within 8 hours of PICU admission to receive a helium-oxygen mixture (helium group) or an air-oxygen mixture (control group) through an inflatable head hood. The primary study outcome was the requirement for positive pressure mechanical ventilation. Results were compared using Fisher's exact test. RESULTS: No differences were noted between the control and helium groups with respect to age (1.0 vs 1.1 months), prematurity, or family history of asthma or smoking. Positive pressure ventilation was judged necessary for 4 of the 21 (19.0%) infants in the control group and in 4 of the 18 (22.2%) in the helium group (relative risk = 1.17; 95% confidence interval = 0.34 to 4.01). CONCLUSIONS: This study did not detect any differences between the patients in the helium group and the control group with respect to the rate of positive-pressure ventilation.

Bronchiolitis, Viral↗